1. Technical Field
The present invention relates to a mounting structure of an electronic component.
2. Related Art
Mounting techniques are used in mounting, on a substrate, electronic components such as semiconductor integrated circuit, when manufacturing liquid crystal devices and a circuit substrate mounted on various electronic apparatuses. A liquid crystal display device, for instance, includes an integrated circuit (IC) chip for liquid crystal drive so as to drive the liquid crystal panel. This IC chip for liquid crystal drive may also be mounted directly on a glass substrate that constitutes the liquid crystal panel, or, may be mounted on a flexible substrate (FPC) which is mounted on the liquid crystal panel. A mounting structure mounted by the former technique is called a chip on glass (COG) structure, and a mounting structure mounted by the latter is called a chip on flexible print circuit (COF) structure. In addition to these mounting structures, a chip on board (COB) structure is known. In this structure, an IC chip is mounted on, for instance, a glass-epoxy substrate.
Substrates and electronic components used for such mounting structures respectively include lands (terminals) coupled to a wiring pattern and bump electrodes for obtaining electric connection. Mounting structures of electronic components are formed by mounting electronic components on the substrates in a state in which the lands are coupled to the bump electrodes.
It has been desired that, in those mounting structures, electronic components be firmly and securely coupled to substrates. Particularly, in the case where there are pluralities of lands and bump electrodes and those lands are coupled to the bump electrodes, it is important that all the lands and bumps are coupled in a preferable manner so as to ensure reliability.
However, since lands and bump electrodes are generally formed with metal, a mispositioning during bonding and a misalignment caused by a low aligning precision of lands and bump electrodes could result in a contact defect (conductive defect) originating from insufficient bonding strength between these lands and bump electrodes.
Moreover, there has been a possibility that a warping of electronic components such as substrates and ICs as well as a fluctuation in setting the height of lands and bump electrodes causes a fluctuation in distance between lands and bump electrodes. This could result in an inability to obtain sufficient bonding strength between the bump electrodes and the terminals, causing a contact defect (conductive defect).
In order to prevent such disadvantages, there has been provided a print circuit board that includes: a conductive pattern having a trapezoid sectional surface; a metal conductive layer formed thereon; and multiple concavities and convexities applied on a surface of this metal conductive layer (refer to JP-A-2002-261407 for an example).
Such a print circuit board is said to provide improved mounting yield, due to the anchoring effect originating from the concavities and convexities on the metal conductive surface. The anchoring effect prevents connecting electrodes of a component (electronic component) from slipping, sliding, and getting inclined on electrodes on the substrate, when pressure is applied during component mounting.
However, while the slipping, the sliding, and the inclination of connecting electrodes (bump electrode) arranged over the metal conductive layer are prevented by the anchor effect that originates from the concavities and convexities of the metal conductive surface, the above-mentioned print circuit board does not have a structure that increases the bonding strength between the metal conductive substrate and the connecting electrode. Further, the structure does not increase the bonding strength of the pluralities of electrodes. Consequently, occurrences of mispositioning during bonding and misalignment of electrodes (lands and bump electrodes) caused by low aligning precision thereof may still result in a contact defect (conductive defect) originating from insufficient bonding strength of these electrodes. Moreover, the connecting electrodes (bump electrodes) are formed with metal, and therefore exhibit plastic deformation upon coupling. This means that, if the distance between the lands and the electrodes were uneven as described above, the connecting electrodes would have a low capability in absorbing the distance deviation by the elastic deformation, and therefore the bonding strength between these electrodes would be insufficient. For this reason, the contact defect (conductive defect) may still occur as well.
Adhesives such as underfills are required to mount and fix components on print circuit boards in a bonding (mounting) structure of print circuit board that includes such a metal conductive layer and a component that includes a connecting electrode, which is one of the causes that inhibits the cost reduction of mounting.